...However, the earthquake in Japan, in addition to damaging the ability of the control rods to regulate the fuel — and the reactor’s coolant system — appears to have damaged the containment facility, and the explosion almost certainly did. There have been reports of “white smoke,” perhaps burning concrete, coming from the scene of the explosion, indicating a containment breach and the almost certain escape of significant amounts of radiation.
At this point, events in Japan bear many similarities to the 1986 Chernobyl disaster. Reports indicate that up to 1.5 meters (4.9 feet) of the reactor fuel was exposed. The reactor fuel appears to have at least partially melted, and the subsequent explosion has shattered the walls and roof of the containment vessel — and likely the remaining useful parts of the control and coolant systems.
It's still possible to contain the mess UNLESS the floor cracked, in which case 'containment' will be impossible.
Pretty high rad-count over there, too, at ~640 rems/hour. That's ~24x 'normal' exposure, with 'normal' being what the average human gets every day from just walking around. NB: See Combox for updates/nuke-engineer recommendations/thoughts.